Docker基础 - 一个web应用实例
通过上文我们已经基本了解了docker的结构（仓库，镜像，容器）以及跑docker应用了；本文将通过介绍一个web应用：向你展示如何进行主机与web容器之间的通信，这是web开发者常用的；第二，贯穿上文中内容, 且为我们后续讲解网络提供基础。@pdai
一个web 应用运行和访问
运行一个 web 应用
我们只需要找一个webapp的镜像即可，无需自己再写个程序啥的。接下来让我们尝试使用 docker 构建一个 web 应用程序。
这里找了一个training/webapp，它是将在docker容器中运行一个 Python Flask web应用。
[root@pdai ~]# docker pull training/webapp
Using default tag: latest
latest: Pulling from training/webapp
Image docker.io/training/webapp:latest uses outdated schema1 manifest format. Please upgrade to a schema2 image for better future compatibility. More information at https://docs.docker.com/registry/spec/deprecated-schema-v1/
e190868d63f8: Pull complete
909cd34c6fd7: Pull complete
0b9bfabab7c1: Pull complete
a3ed95caeb02: Pull complete
10bbbc0fc0ff: Pull complete
fca59b508e9f: Pull complete
e7ae2541b15b: Pull complete
9dd97ef58ce9: Pull complete
a4c1b0cb7af7: Pull complete
Digest: sha256:06e9c1983bd6d5db5fba376ccd63bfa529e8d02f23d5079b8f74a616308fb11d
Status: Downloaded newer image for training/webapp:latest
docker.io/training/webapp:latest
[root@pdai ~]# docker images | grep webapp
training/webapp latest 6fae60ef3446 4 years ago 349MB
紧接着，我们启动这个webapp
[root@pdai ~]# docker run -d -P training/webapp python app.py
ec3eb9ae218494d5aa5902c1ca4435733567b5e81319f02e5d2509d45cbc25da
[root@pdai ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ec3eb9ae2184 training/webapp "python app.py" 18 seconds ago Up 17 seconds 0.0.0.0:32768->5000/tcp gifted_agnesi
参数说明:
-d:让容器在后台运行。-P:将容器内部使用的网络端口映射到我们使用的主机上。
访问webapp
我们注意看上述PORTS部分为0.0.0.0:32769->5000/tcp
Docker 开放了 5000 端口（默认 Python Flask 端口）映射到主机端口 32768 上。
- 从主机上看，它应该暴露了端口32768
所以我们来验证下：
[root@pdai ~]# netstat | grep 32768
[root@pdai ~]# netstat -nltp | grep 32768
tcp6 0 0 :::32768 :::* LISTEN 2227/docker-proxy
[root@pdai ~]# curl localhost:32768
Hello world!
这意味着，你浏览器你可以输入localhost:32768访问这个页面。
- 从容器内部看，它应该有一个端口5000
我们再进容器验证下：
[root@pdai ~]# docker exec -it ec3eb9ae2184 /bin/bash
root@ec3eb9ae2184:/opt/webapp# netstat -nltp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:5000 0.0.0.0:* LISTEN 1/python
所以我们的理解是对的。
设置自定义映射端口
我们发现，通过
-P参数映射到主机上的端口是随机，能否自定义端口呢？
我们可以通过 -p 参数来设置不一样的端口；为了对比，我们再起一个容器实例：
[root@pdai ~]# docker run -d -p 5001:5000 training/webapp python app.py
5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a
[root@pdai ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
5da3588d5bc4 training/webapp "python app.py" 33 seconds ago Up 31 seconds 0.0.0.0:5001->5000/tcp hopeful_bardeen
ec3eb9ae2184 training/webapp "python app.py" 22 minutes ago Up 22 minutes 0.0.0.0:32768->5000/tcp gifted_agnesi
[root@pdai ~]# netstat -nltp | grep 5001
tcp6 0 0 :::5001 :::* LISTEN 2591/docker-proxy
[root@pdai ~]# curl localhost:5001
Hello world!
所以你看到跑了两个内部端口都是5000的web实例，新的容器内部的 5000 端口映射到我们本地主机的 5001 端口上。
其它常用功能
查看web 应用网络端口
通过 docker ps 命令可以查看到容器的端口映射，docker 还提供了另一个快捷方式 docker port，使用 docker port 可以查看指定 （ID 或者名字）容器的某个确定端口映射到宿主机的端口号。
上面我们创建的 web 应用容器 ID 为 5da3588d5bc4 名字为 hopeful_bardeen。
我可以这样查看容器端口的映射情况：
[root@pdai ~]# docker port 5da3588d5bc4
5000/tcp -> 0.0.0.0:5001
[root@pdai ~]# docker port hopeful_bardeen
5000/tcp -> 0.0.0.0:5001
查看 WEB 应用程序日志
docker logs [ID或者名字] 可以查看容器内部的标准输出。
[root@pdai ~]# docker port hopeful_bardeen
5000/tcp -> 0.0.0.0:5001
[root@pdai ~]# docker logs -f hopeful_bardeen
* Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
172.17.0.1 - - [18/Feb/2020 09:08:31] "GET / HTTP/1.1" 200 -
^C
参数说明：
-f: 让 docker logs 像使用 tail -f 一样来输出容器内部的标准输出。
从上面，我们可以看到应用程序使用的是 5000 端口并且能够查看到应用程序的访问日志。
查看WEB应用程序容器的进程
我们还可以使用 docker top 来查看容器内部运行的进程
[root@pdai ~]# docker top hopeful_bardeen
UID PID PPID C STIME TTY TIME CMD
root 2614 2597 0 17:07 ? 00:00:00 python app.py
检查 WEB 应用程序
使用 docker inspect 来查看 Docker 的底层信息。它会返回一个 JSON 文件记录着 Docker 容器的配置和状态信息。
[root@pdai ~]# docker inspect hopeful_bardeen
[
{
"Id": "5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a",
"Created": "2020-02-18T09:07:32.827193286Z",
"Path": "python",
"Args": [
"app.py"
],
"State": {
"Status": "running",
"Running": true,
"Paused": false,
"Restarting": false,
"OOMKilled": false,
"Dead": false,
"Pid": 2614,
"ExitCode": 0,
"Error": "",
"StartedAt": "2020-02-18T09:07:33.374368448Z",
"FinishedAt": "0001-01-01T00:00:00Z"
},
"Image": "sha256:6fae60ef344644649a39240b94d73b8ba9c67f898ede85cf8e947a887b3e6557",
"ResolvConfPath": "/var/lib/docker/containers/5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a/resolv.conf",
"HostnamePath": "/var/lib/docker/containers/5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a/hostname",
"HostsPath": "/var/lib/docker/containers/5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a/hosts",
"LogPath": "/var/lib/docker/containers/5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a/5da3588d5bc43a9ed3aa61fb87f98220c9719d2879b616404d443aaae6cee77a-json.log",
"Name": "/hopeful_bardeen",
"RestartCount": 0,
"Driver": "overlay2",
"Platform": "linux",
"MountLabel": "",
"ProcessLabel": "",
"AppArmorProfile": "",
"ExecIDs": null,
"HostConfig": {
"Binds": null,
"ContainerIDFile": "",
"LogConfig": {
"Type": "json-file",
"Config": {}
},
"NetworkMode": "default",
"PortBindings": {
"5000/tcp": [
{
"HostIp": "",
"HostPort": "5001"
}
]
},
"RestartPolicy": {
"Name": "no",
"MaximumRetryCount": 0
},
"AutoRemove": false,
"VolumeDriver": "",
"VolumesFrom": null,
"CapAdd": null,
"CapDrop": null,
"Capabilities": null,
"Dns": [],
"DnsOptions": [],
"DnsSearch": [],
"ExtraHosts": null,
"GroupAdd": null,
"IpcMode": "private",
"Cgroup": "",
"Links": null,
"OomScoreAdj": 0,
"PidMode": "",
"Privileged": false,
"PublishAllPorts": false,
"ReadonlyRootfs": false,
"SecurityOpt": null,
"UTSMode": "",
"UsernsMode": "",
"ShmSize": 67108864,
"Runtime": "runc",
"ConsoleSize": [
0,
0
],
"Isolation": "",
"CpuShares": 0,
"Memory": 0,
"NanoCpus": 0,
"CgroupParent": "",
"BlkioWeight": 0,
"BlkioWeightDevice": [],
"BlkioDeviceReadBps": null,
"BlkioDeviceWriteBps": null,
"BlkioDeviceReadIOps": null,
"BlkioDeviceWriteIOps": null,
"CpuPeriod": 0,
"CpuQuota": 0,
"CpuRealtimePeriod": 0,
"CpuRealtimeRuntime": 0,
"CpusetCpus": "",
"CpusetMems": "",
"Devices": [],
"DeviceCgroupRules": null,
"DeviceRequests": null,
"KernelMemory": 0,
"KernelMemoryTCP": 0,
"MemoryReservation": 0,
"MemorySwap": 0,
"MemorySwappiness": null,
"OomKillDisable": false,
"PidsLimit": null,
"Ulimits": null,
"CpuCount": 0,
"CpuPercent": 0,
"IOMaximumIOps": 0,
"IOMaximumBandwidth": 0,
"MaskedPaths": [
"/proc/asound",
"/proc/acpi",
"/proc/kcore",
"/proc/keys",
"/proc/latency_stats",
"/proc/timer_list",
"/proc/timer_stats",
"/proc/sched_debug",
"/proc/scsi",
"/sys/firmware"
],
"ReadonlyPaths": [
"/proc/bus",
"/proc/fs",
"/proc/irq",
"/proc/sys",
"/proc/sysrq-trigger"
]
},
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/c6594e5b70feca02eb4b90ac75aba711f36378d5cb9853ffca1ec92f9d0c3e14-init/diff:/var/lib/docker/overlay2/d4690a06236a3857a2a51ab84c61992e50ea3e1a613f4793334916604ea0dfa0/diff:/var/lib/docker/overlay2/c45d0215cd2076174f38fea5003c3ff11a5ba2df2141d9d069f4bf32dac9a22a/diff:/var/lib/docker/overlay2/1cf63068912234a1f4c861f58f155423c87193c6e438948db493687d4da4f0a0/diff:/var/lib/docker/overlay2/55e4ecb04b1ff8d048bc75bb8698c782c813d45caa6f0d82ac6c49adec24bead/diff:/var/lib/docker/overlay2/27fa0dc314b851b8d2f0386d230a725f57117f9f1ccdb49ca27f5ad424cb4a90/diff:/var/lib/docker/overlay2/65a5a082188d9e0b9aaf09c2e9c3b3f8141f74c781996680dfaca63d81672cdf/diff:/var/lib/docker/overlay2/658a33c92cf114ee4cbc10f117207a0c813e39a908acc014fbce1783a28bc654/diff:/var/lib/docker/overlay2/e5b5c9e0abc43ff2750dcd33decc65d90d733b18f2626b91c500d803d7fe189b/diff:/var/lib/docker/overlay2/0b5181e429a89f6ab291e090b972e11718e4f63158ed60af1fce18095d0352a6/diff:/var/lib/docker/overlay2/f7c0405739bb58fdfa9af402a72507b78bc2a48b0d74356dad59495906b6e0e5/diff:/var/lib/docker/overlay2/073c45ae4a6ff27950a1dd969a675d3dcdc18392bb205ddde5913fcc10a751ef/diff:/var/lib/docker/overlay2/f92534844c8cc5b950ea36369b8e4a7dd7f7749e73483908e5d129bf5c26442f/diff:/var/lib/docker/overlay2/477378381d03c4b347d7b9224c4c9023b5dfbfde32022c7eb8af32e7a01b88b2/diff",
"MergedDir": "/var/lib/docker/overlay2/c6594e5b70feca02eb4b90ac75aba711f36378d5cb9853ffca1ec92f9d0c3e14/merged",
"UpperDir": "/var/lib/docker/overlay2/c6594e5b70feca02eb4b90ac75aba711f36378d5cb9853ffca1ec92f9d0c3e14/diff",
"WorkDir": "/var/lib/docker/overlay2/c6594e5b70feca02eb4b90ac75aba711f36378d5cb9853ffca1ec92f9d0c3e14/work"
},
"Name": "overlay2"
},
"Mounts": [],
"Config": {
"Hostname": "5da3588d5bc4",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"5000/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"python",
"app.py"
],
"Image": "training/webapp",
"Volumes": null,
"WorkingDir": "/opt/webapp",
"Entrypoint": null,
"OnBuild": null,
"Labels": {}
},
"NetworkSettings": {
"Bridge": "",
"SandboxID": "66e1f111a5d7acca71f0e9e24516a6945bca428f55ac1eab1576c99bde16190c",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {
"5000/tcp": [
{
"HostIp": "0.0.0.0",
"HostPort": "5001"
}
]
},
"SandboxKey": "/var/run/docker/netns/66e1f111a5d7",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "794d5e97cd3bbb62c8a7a850f125404d174ecc45df4e704dbee403b1be7a2835",
"Gateway": "172.17.0.1",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "172.17.0.3",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"MacAddress": "02:42:ac:11:00:03",
"Networks": {
"bridge": {
"IPAMConfig": null,
"Links": null,
"Aliases": null,
"NetworkID": "b8c5abdb0becacfa1bfa1d72e2e663fb0157b62a9b8bee37e2607211722713cc",
"EndpointID": "794d5e97cd3bbb62c8a7a850f125404d174ecc45df4e704dbee403b1be7a2835",
"Gateway": "172.17.0.1",
"IPAddress": "172.17.0.3",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:ac:11:00:03",
"DriverOpts": null
}
}
}
}
]
停止 WEB 应用容器
再复习下docker的停止
[root@pdai ~]# docker stop hopeful_bardeen
hopeful_bardeen
[root@pdai ~]# docker ps -a | grep 'hopeful_bardeen'
5da3588d5bc4 training/webapp "python app.py" 13 minutes ago Exited (137) 12 seconds ago hopeful_bardeen
重启WEB应用容器
已经停止的容器，我们可以使用命令 docker start 或者docker restart 来启动。
[root@pdai ~]# docker restart hopeful_bardeen
hopeful_bardeen
[root@pdai ~]# docker ps -a | grep hopeful_bardeen
5da3588d5bc4 training/webapp "python app.py" 14 minutes ago Up 10 seconds 0.0.0.0:5001->5000/tcp hopeful_bardeen
移除WEB应用容器
我们可以使用 docker rm 命令来删除不需要的容器
我们上文也讲过，如果是启动着的docker实例，需要加-f，强制（force）删除。
[root@pdai ~]# docker ps -a | grep hopeful_bardeen
5da3588d5bc4 training/webapp "python app.py" 14 minutes ago Up 10 seconds 0.0.0.0:5001->5000/tcp hopeful_bardeen
[root@pdai ~]# docker rm -f hopeful_bardeen
hopeful_bardeen
[root@pdai ~]# docker ps -a | grep hopeful_bardeen
[root@pdai ~]#
与其它容器（DB容器）互联
上述是一个web单一容器通过端口映射，可以通过主机端口访问容器；那么如果需要访问数据库，就涉及到容器互联。
与数据库容器互联
- 先停止上述的web容器, 且清理所有不用的容器
[root@pdai ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ec3eb9ae2184 training/webapp "python app.py" 18 hours ago Up 18 hours 0.0.0.0:32768->5000/tcp gifted_agnesi
11de9755a084 pdai/ubuntu:v2.0.2 "/bin/bash" 24 hours ago Exited (0) 24 hours ago pdai-ubuntu-202
57bd797570b6 pdai/ubuntu:v2.0.2 "--name pdai-test" 24 hours ago Created sharp_brahmagupta
[root@pdai ~]# docker stop ec3eb9ae2184
ec3eb9ae2184
[root@pdai ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ec3eb9ae2184 training/webapp "python app.py" 18 hours ago Exited (137) 29 seconds ago gifted_agnesi
11de9755a084 pdai/ubuntu:v2.0.2 "/bin/bash" 24 hours ago Exited (0) 24 hours ago pdai-ubuntu-202
57bd797570b6 pdai/ubuntu:v2.0.2 "--name pdai-test" 24 hours ago Created sharp_brahmagupta
[root@pdai ~]# docker container prune
WARNING! This will remove all stopped containers.
Are you sure you want to continue? [y/N] y
Deleted Containers:
ec3eb9ae218494d5aa5902c1ca4435733567b5e81319f02e5d2509d45cbc25da
11de9755a08402d963d263a559a7daf48f4a2188398f258641240b5eb50fbc89
57bd797570b68b6587b16809889e6e8f710ec7a934229aa6391add02f758e036
Total reclaimed space: 89B
[root@pdai ~]#
- 创建一个新的数据库容器。
[root@pdai ~]# docker run -d --name db training/postgres
Unable to find image 'training/postgres:latest' locally
latest: Pulling from training/postgres
Image docker.io/training/postgres:latest uses outdated schema1 manifest format. Please upgrade to a schema2 image for better future compatibility. More information at https://docs.docker.com/registry/spec/deprecated-schema-v1/
a3ed95caeb02: Pull complete
6e71c809542e: Pull complete
2978d9af87ba: Pull complete
e1bca35b062f: Pull complete
500b6decf741: Pull complete
74b14ef2151f: Pull complete
7afd5ed3826e: Pull complete
3c69bb244f5e: Pull complete
d86f9ec5aedf: Pull complete
010fabf20157: Pull complete
Digest: sha256:a945dc6dcfbc8d009c3d972931608344b76c2870ce796da00a827bd50791907e
Status: Downloaded newer image for training/postgres:latest
d992e3c761e00649eb436b88c737adc54093b76119af0fb7878596b523f743ca
[root@pdai ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d992e3c761e0 training/postgres "su postgres -c '/us…" 9 seconds ago Up 7 seconds 5432/tcp db
- db 容器和 web 容器建立互联关系
[root@pdai ~]# docker run -d -p 5001:5000 --name web --link db:db training/webapp python app.py
1cbc9aeba2a8a826d460ecb49de17ddf8ac336e150c752a3c762fd38a3e15254
[root@pdai ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1cbc9aeba2a8 training/webapp "python app.py" 5 seconds ago Up 4 seconds 0.0.0.0:5001->5000/tcp web
d992e3c761e0 training/postgres "su postgres -c '/us…" 7 minutes ago Up 7 minutes 5432/tcp db
--link 参数的格式为 --link name:alias，其中 name 是要链接的容器的名称，alias 是这个连接的别名。
Docker 在两个互联的容器之间创建了一个安全隧道，而且不用映射它们的端口到宿主主机上。在启动 db 容器的时候并没有使用 -p 和 -P 标记，从而避免了暴露数据库端口到外部网络上。
容器公开的连接信息
Docker 通过 2 种方式为容器公开连接信息：
- 环境变量
- 更新 /etc/hosts 文件
环境变量
使用 env 命令来查看 web 容器的环境变量
[root@pdai ~]# docker exec -it web /bin/bash
root@1cbc9aeba2a8:/opt/webapp# env
HOSTNAME=1cbc9aeba2a8
DB_NAME=/web/db
DB_PORT_5432_TCP_ADDR=172.17.0.2
DB_PORT=tcp://172.17.0.2:5432
DB_PORT_5432_TCP=tcp://172.17.0.2:5432
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/opt/webapp
DB_PORT_5432_TCP_PORT=5432
SHLVL=1
HOME=/root
DB_PORT_5432_TCP_PROTO=tcp
DB_ENV_PG_VERSION=9.3
_=/usr/bin/env
其中 DB_ 开头的环境变量是供 web 容器连接 db 容器使用，前缀采用大写的连接别名。
hosts 文件
除了环境变量，Docker 还添加 host 信息到父容器的 /etc/hosts 的文件。下面是父容器 web 的 hosts 文件
root@1cbc9aeba2a8:/opt/webapp# cat /etc/hosts
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.2 db d992e3c761e0
172.17.0.3 1cbc9aeba2a8
root@1cbc9aeba2a8:/opt/webapp#
这里有 2 个 hosts:
- 第一个,
172.17.0.2 db d992e3c761e0表示 db 容器的 ip, ID和Name - 第二个，
172.17.0.3 1cbc9aeba2a8表示 web 容器的 ip, ID
可以在 web 容器中安装 ping 命令来测试跟db容器的连通。
root@1cbc9aeba2a8:/opt/webapp# apt-get install -yqq inetutils-ping
(Reading database ... 18233 files and directories currently installed.)
Removing ubuntu-minimal (1.325) ...
Removing iputils-ping (3:20121221-4ubuntu1.1) ...
Selecting previously unselected package inetutils-ping.
(Reading database ... 18221 files and directories currently installed.)
Preparing to unpack .../inetutils-ping_2%3a1.9.2-1_amd64.deb ...
Unpacking inetutils-ping (2:1.9.2-1) ...
Setting up inetutils-ping (2:1.9.2-1) ...
root@1cbc9aeba2a8:/opt/webapp# ping db
PING db (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: icmp_seq=0 ttl=64 time=0.110 ms
64 bytes from 172.17.0.2: icmp_seq=1 ttl=64 time=0.092 ms
64 bytes from 172.17.0.2: icmp_seq=2 ttl=64 time=0.094 ms
64 bytes from 172.17.0.2: icmp_seq=3 ttl=64 time=0.104 ms
64 bytes from 172.17.0.2: icmp_seq=4 ttl=64 time=0.111 ms
64 bytes from 172.17.0.2: icmp_seq=5 ttl=64 time=0.093 ms
64 bytes from 172.17.0.2: icmp_seq=6 ttl=64 time=0.095 ms
^C--- db ping statistics ---
7 packets transmitted, 7 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.092/0.100/0.111/0.000 ms
用 ping 来测试db容器，它会解析成 172.17.0.2。
当然，你还可以ping db容器的ID或者内部IP, 结果是一样的。
root@1cbc9aeba2a8:/opt/webapp# ping -t 4 d992e3c761e0
ping: unsupported packet type: 4
root@1cbc9aeba2a8:/opt/webapp# ping d992e3c761e0
PING db (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: icmp_seq=0 ttl=64 time=0.089 ms
64 bytes from 172.17.0.2: icmp_seq=1 ttl=64 time=0.093 ms
^C--- db ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.089/0.091/0.093/0.000 ms
root@1cbc9aeba2a8:/opt/webapp# ping 172.17.0.2
PING 172.17.0.2 (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: icmp_seq=0 ttl=64 time=0.094 ms
64 bytes from 172.17.0.2: icmp_seq=1 ttl=64 time=0.103 ms
^C--- 172.17.0.2 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.094/0.099/0.103/0.000 ms
root@1cbc9aeba2a8:/opt/webapp#
用户可以链接多个父容器到子容器，比如可以链接多个 web 到 db 容器上。